Methods of preparing a toner for developing electrostatic latent image, used in image forming apparatuses such as electrophotographic copiers, printers, facsimile and their complex machines have been mostly pulverization methods, but polymerization methods have been more used recently. The polymerization method is so called because of forming a particulate toner in an aqueous medium and including a polymerization reaction of toner materials when forming the particulate toner or in the process thereof. The polymerization methods include suspension polymerization methods, emulsification aggregation methods, polymer suspension (aggregation) methods and ester elongation methods. Atoner prepared by the polymerization methods is called a polymerization toner or a chemical toner.
The polymerization toner typically has smaller particle diameter, a narrower particle diameter distribution and more spherical shape than the pulverization toner. This is why the polymerization toner produces higher quality images in electrophotography. However, the polymerization toner needs a long time in the polymerization process, further needs separating a toner from a solvent after solidified, and then repeating washing and drying, resulting in disadvantages of needing much timer, water and energy.
Japanese Patents Nos. 3786034 and 3786035 (relevant to Japanese published unexamined applications Nos. 2003-262976 and 2003-262977, respectively) and Japanese published unexamined applications Nos. 57-201248 and 2006-293320 disclose toner preparation methods called spray granulation methods discharging a liquid (toner component liquid) including toner materials dissolved or dispersed in an organic solvent with an atomizer so as to become a microscopic droplet and drying the droplet to prepare a particulate toner. This method does not need using water and largely reduces time for washing and drying.
When a particulate such as a toner is produced by the spray granulation methods, it is preferable to project a droplet of a liquid including a particulate component such as a toner component liquid from a projection hole of a droplet projector and solidify the droplet. Conventional inkjet recording technology can be used to precisely control the size of the droplet projected from the projection hole of the droplet projector, and therefore the particle diameter of the particulate can precisely be controlled.
However, the droplet is not properly projected from the projection hole occasionally when starting discharging. This is because the liquid including a particulate component covering an exit of the projection hole is dried until starting discharging to increase viscosity or the liquid including a particulate component is dried and solidified to block the projection hole. The projection hole incapable of properly discharging a droplet when starting discharging is not restored even if driven to continue discharging. Therefore, such a projection hole incapable of properly discharging a droplet decreases productivity of the particulate.
Even if the droplet is properly projected from the projection hole at the beginning, the liquid including a particulate component covering an exit of the projection hole is dried to increase viscosity or partially solidified to block the projection hole while projected, the droplet is likely not to be properly projected, resulting in decrease of productivity of the particulate.
In order to continue properly discharging a droplet, a method of stopping the projection hole from discharging and washing the hole to restore projectability of the hole incapable of properly discharging the droplet can be thought. However, the productivity of the particulate decreases because of not being produced while the projection hole is washed.
Because of these reasons, a need exist for a method capable of improving productivity of particulate when discharging a droplet of a liquid including a particulate component from a projection hole of a droplet projector to produce a particulate.